He could join another party, in which case his membership of New Zealand First would automatically be terminated. At this point this looks highly unlikely, for it is difficult to see why any other party would invite him inside their own tent. He might also establish a new party. Peters did this in 1993 when he left National and formed New Zealand First.
But the most likely outcome is that the party's board will vote to expel him. There are several grounds on which any member of New Zealand First can be expelled by a majority decision of the board, including one which concerns actions inconsistent with the welfare and interest of the party.
That would seem to describe the effects of Horan's alleged behaviour nicely.
But even if Horan is expelled from the party, he can remain an MP, because the relevant statutory provisions (section 55 of the Electoral Act 1993) do not allow a political party to remove a member of parliament.
There are various grounds on which a vacancy in the House of Representatives can be created (such as taking an oath of allegiance to a foreign state, ceasing to be a New Zealand citizen, or being convicted of a crime punishable by a prison term of two years or more).
But leaving the party on whose ticket you were elected is not one of them.
Between 2001 and 2005 that was not the case. After the defection of a number of so-called "party hoppers" (who joined another party) or "waka jumpers" (who chose independence) between 1996 and 1999, the law was changed so that an MP who left or was biffed out of a party's caucus also ceased to be an MP. But that provision lapsed in September 2005, so there is now no legal way in which Winston Peters or anyone else can force Brendan Horan to vacate his seat.
Your feelings about this are likely to depend on your views on the responsibilities of MPs.
Those who think MPs are primarily accountable to their parties are likely to oppose the present legal situation.
But those of the persuasion that an MP's obligations are first and foremost to the voters who elect them (either directly in the case of constituency MPs or indirectly via the party vote for list MPs) could argue that a return to the old waka-hopping law would give political parties too much control over MPs.
This may be fine if an MP has done something terribly wrong - but it could also lead to the abuse of power by a party's leadership by, for instance, silencing dissenting voices within a party.
In any event, changing the law may not be the best way to resolve this issue. It could produce protracted legal action that, as in the case of former Act MP Donna Awatere-Huata, goes all the way to the Supreme Court.
As Pansy Wong, Phillip Field and Chris Carter might attest, going solo in Parliament can be a miserable sort of existence.
Horan will need all the resilience he developed in his days as a professional lifeguard if he is to survive it.
- Associate Professor Richard Shaw is the associate head of Massey's School of People, Environment and Planning.
